Contour Plywood Plate

[richiehamilton]

Hi all

I've been thinking for a while that I'd really like to make something like an E-335 or even gretsch style hollow electric. these generally have formed plywood tops and backs. Has anyone tried moulding their own plywood for this, or has anyone an idea as to how to try it? I presume they are normally formed in some sort of press, and steamed while it's tightened. Would a wooden press made of criss-crossed horizontal and vertical sections work? Any suggestions?

Thanks a lot

Richie

Edited June 21, 2007 by richiehamilton

[GoodWood]

Hi all

I've been thinking for a while that I'd really like to make something like an E-335 or even gretsch style hollow electric. these generally have formed plywood tops and backs. Has anyone tried moulding their own plywood for this, or has anyone an idea as to how to try it? I presume they are normally formed in some sort of press, and steamed while it's tightened. Would a wooden press made of criss-crossed horizontal and vertical sections work? Any suggestions?

Thanks a lot

Richie

I think if you had a positive and negative mold it could work with regular wood, plywood might fall apart. Even a strong plaster mold might work, but you would need at least 2 heat blankets at 136.00 a piece. I think Ive seen carved mandolin tops and I think you can buy a partially shaped top wiht the hard work done, google, or stewi mac might be the mandolin tops.

If you have to hand carve it it would be like doing a large violin. It would take alot of time the first couple times

[erikbojerik]

Even a strong plaster mold might work

No way...bad bad bad. I wouldn't make the form from plywood either.

I think you might get this to work if you made a contoured template from a single piece of really thick, hard large stable hardwood, heating blankets as was mentioned, and put the whole works into a big vacuum bag (but one that won't melt at 250°C....).

Good luck. You could carve a dozen tops by hand with an angle grinder before you got that system to work. An angle grinder is ~$30.

Get Bob Benedetto's book, forget about laminated tops, and make a real archtop.

[tim_ado]

yeah i have a hollow body with a contoured top and i cant tell u it was carved out of some nice flamed maple

i wouldnt use ply wood at all and the steam press(even if it did work) would probaly be expensive and alot of hasel i woul just carve it

plus carvings funner

[another doug]

I am not even close to being an expert on this (I've certainly never done it), but I do have a couple thoughts on the subject:

1- In my opinion, there's nothing inherently wrong with vacuum formed laminated tops; plenty of highly respected makers use the technique. However, if you're looking to make a true (acoustic) archtop, you'll want to carve. Plus, carving would be easier and cheaper in terms of the tools required.

2- It's important to note that you're not taking plywood and forming it into the shape; you're taking a number of veneers, and pressing and gluing them together to make the laminate (or "plywood"). Pretty sure you need a solid mold and vacuum press to do it, although goodwood's suggestion may also work.

3- tim, unless you can see that the wood is solid (i.e. looking at an unbound f-hole or pickup rout) it's completely possible that your archtop is a laminate with a very nice veneer on top. I'm not saying that it IS a laminate, just that it could be.

4- richie- if you're sure you want to try this, you'll probably want to check out the MIMF. If the answer is out there, that's where you'll find it (not saying that no one here knows, but they're more geared toward acoustics and archtops).

Just my (2x4=) 8 cents

Doug

[GoodWood]

http://www.stewmac.com/shop/Bodies,_necks,..._and_sides.html

They precarve the backs, not the tops, but there might be someone with a CNC out there for tops. That is why hes wanting a mold I assume.

If you can sculpt clay or are good with wood, (See lute builing for form information) then you could do a build up ply top I guess. Sculpting in clay then cast in plaster with hemp filler. Fairly cheap and easy You r gonna need that book also, get the book and see how bad it is. Carving tops is a specialty.

[tim_ado]

3- tim, unless you can see that the wood is solid (i.e. looking at an unbound f-hole or pickup rout) it's completely possible that your archtop is a laminate with a very nice veneer on top. I'm not saying that it IS a laminate, just that it could be.

nope i can see its full maple.........i guess there was an upside to having some of the binding chip off

[brian d]

FWIW, in the Koch book he doesn't precarve or pre-shape the top for this style of construction. He uses a thin top-plate (2mm) which is flexible enough to take on the arch shape as defined by the sustain block and sides/linings. In the example shown in the book he uses birch plywood, but he says you can use solid wood too.

I haven't tried it (though I intend to).

Brian

[Acousticraft]

I used 1/8" thick maple top and back for my 335 copy that I thicknessed down and joined. I then radiused the centre block in both planes. Then I made a full clamping ring the shape of the guitar and clamped it with many clamps and it pulled it down tight and it gave a nice even arch. With Mahogany body and Maple front and back it has a real nice sound with full bass and sweet treble.

I glued the back first so i could clean out any excess glue so when you look thru the F holes it looks nice and clean.

Edited June 29, 2007 by Acousticraft

[Myka Guitars]

I was just thinking about this again this morning. I have some highly figured Bolivian rosewood veneer that is screaming to become a 335-ish guitar.

I have some experience with mold making and plaster casting. I used to be a model and mold maker for a terra cotta restoration company (BVTC and we used several types of plaster. Regular plaster of Paris that you might get from the hardware store will not work unless you reinforce it with glass fiber or some other binding fibers (burlap or chicken wire works great too). This type of plaster along with Pottery No.1 and other similar white plasters (you can find them here: ClayMaker.com) are not designed for the pressures of die making and they will most likely fail unless the are either 3-4" thick or are backed up with at least a 1/2" steel plate. The reason is that most people do not have hydraulic presses at their disposal which evenly distribute pressure on the die. So the most common method of clamping the two halves together will more than likely be a series of clamps along the perimeter of the die. Without fail this will eventually crack the die even with reinforcement.

If you are dead set on the die idea then a better solution is to find a harder casting plaster like Ceramical, UltraCal, or Hydrostone. These are designed for industrial dies and tooling (you can find some here: GypsumSolutions distributors). The stuff is not cheap and you must use fresh plaster (>90 days old) and you must let it dry completely. Failure to let it dry completely will result in a partially cured block of plaster. If you don't have a drying oven then you must wait a week or so depending on how thick the mold is and the humidity. When properly dried Ceramical is like, ...ceramic. Hard and strong but still very brittle. If you make it right you can make a plaster die that will hold up to the pressure of forming plywood tops but they dies will still be very heavy and large unless they are backed up sufficiently with a flat backer or poured into a steel frame.

My whole point is that making a two part die is a pretty involved process and if a lasting mold or die is desired it is beyond what you can find at the hardware store. If you wanted something to last it will require a good steel frame for the dies that are internally supported by rebar or something like that.

If you wanted to use a one piece mold to form the veneer over and use a vacuum bag system then this can work. I have successfully formed veneer over the top of a carved spruce archtop with a vacuum system. The process could easily be modified to use a carved form (made from MDF, plywood, wood, etc) or a plaster mold. The plaster will still need to be thick but since it will be inside the vacuum bag it will not be under as much stress as a two piece mold. Then it is a matter of lining up your veneers and pulling a vacuum. This is how I plan to make my tops.

Contrary to popular belief a plywood top is not a cheap way of building an archtop. It all depends on how well the top is made and the quality of the materials. I prefer the sound of a solid wood 335-style guitar but the laminated top has its place.

For a great resource on vacuum presses check out joewoodworker.com. I bought a reconditioned vacuum pump (these are a steal), a 24" square bag, a water trap, a couple of valves (so I didn't have to use a regulator), and a hose. The two valves work to shut off airflow to the bag (to seal after a vacuum is pulled) and the other is to release the line pressure at the pump so it can start (most pumps cannot start under a vacuum). If you wanted a continuous running system then you need the reservoirs, regulators, etc. I use Titebond which sets up fast so I made a dirt simple system instead.

Places like certainlywood.com often have maple veneer that is 15"-20" wide, perfect for just about any archtop. They are a great company because they have a minimum purchase of one piece.

FWIW, in the Koch book he doesn't precarve or pre-shape the top for this style of construction. He uses a thin top-plate (2mm) which is flexible enough to take on the arch shape as defined by the sustain block and sides/linings. In the example shown in the book he uses birch plywood, but he says you can use solid wood too.

BEWARE! I also have some experience with this too. This method is a recipe for disaster. I tried this on a guitar years ago (15+) and the pressure from the flat plate being forced into an arch at the sides was enough to pull the guitar apart after only 3 years. The problem is that the angle from the side to the top is kept at 90 degrees which really torques the wood. I would not try this method unless you have a few years to see the results (and wood to burn).

In contrast to this method is the domed acoustic top. This method carries the angle of the arch onto the sides to form a perfectly matched gluing surface. There is very little stress on the side/top joint and there are no rotational stresses to worry about.

~David

[brian d]

In contrast to this method is the domed acoustic top. This method carries the angle of the arch onto the sides to form a perfectly matched gluing surface. There is very little stress on the side/top joint and there are no rotational stresses to worry about.

~David

The domed acoustic top (and back for that matter) also have the radiused braces holding the subtle curve.

David, do you think that if I carried the arch onto the linings for a 335 type build and did away with the 'recurve' it would be more stable? (I prefer the smoother non-recurved look anyway) Or do you need those braces holding the curve to reduce the stress on the joint?

Cheers,

Brian.

[Acousticraft]

I think the point made about a thin top being forced into shape with a traditional thin side, kerfed lining construction would be correct as the built in stress is high and would deform and pull apart over time.

I cut my body out of a 1-3/4" thick piece of Mahogany then cut out the inside with a bandsaw leaving 1" around the edges plus the center block. The center block section then can have its profile block cut out and glued on front and back to make the total thickness about 2-1/2". Then its a matter of sanding and shaping them so when the top/bottom is forced down and glued it will conform to a nice smooth arch shape. The Maple I used did this with ease although I found had to clamp the centre block area first before pulling the edges down otherwise it will try to split on the middle join.

Once everything is clamped snug and the glue has dried there is a big gluing surface to hold the stresses.

The piece of Mahogany I used was heavy so the finished guitar is really heavy but has fantastic sustain. I gig with it regularly and hardly notice the weight now.

When I make another I will probably cut out the excess wood not needed in the center block area behind the tail-piece and thin the sides down to reduce weight. The Maple offcuts from front/back were used to bind the fingerboard.

http://s54.photobucket.com/albums/g111/One...Image0002-1.jpg

Edited June 30, 2007 by Acousticraft

[Myka Guitars]

David, do you think that if I carried the arch onto the linings for a 335 type build and did away with the 'recurve' it would be more stable? (I prefer the smoother non-recurved look anyway) Or do you need those braces holding the curve to reduce the stress on the joint?

It would be more stable because you would not have unprecdictable stresses acting upon the guitar. Whenever you stress a piece of wood there is a long term effect no matter how slight. The curved braces in a acoustic do help to hold the shape and spread out the overall stress. But a slight dome to a top takes much less force to form than a forced recurve shape.

Acousticraft, I agree that a 1" gluing area around the perimeter pretty much reduces the chance of it pulling apart at the joint to 0%. You do illustrate my point however by stating that the middle join wanted to break when you forced the bend and you had to glue it first to prevent that. Regardless of that there is still a lot of unresolved tension in the wood top. It will either relax over time or you may find some cracks developing (perhaps near the f-holes). I suppose bracing it could force it further but I would not recommend forcing wood to do something it doesn't want to do. The results are always unpredictable. Good luck with it.

~David

Edited June 30, 2007 by Myka Guitars

[richiehamilton]

Ok thanks all.

I think in hindsight it might well be easier to just carve the solid wood in the old fashioned archtop style. Although I love carving, something about the cheapness of many factory run guitars appeals to me. However it is probably true that by the time you get any sort of press system to work you could have carved plenty of guitars. I hadn't considered a grinder for rough material removal before though, can anyone direct me to a photo essay or pictures of someone actually doing this? Thanks everyone for all the replies, and I'll probably stick to the old way.

richie

[Vinny]

Funny thing that this topic happened to come up as Im about to clamp down a 3/16 birch ply top on my ES175 style hollowbody. Ive been looking at the arch I have in the center block and Im worried that It'll split the birch when its clamped down. The ply bends great with the grain, but across the grain it wants to split easily. Add to that the fact that the body's kerf-lined edge is flat across, so this birch will have to do a helluva dance to stay glued down. I see no other option but to reduce the arch to the bare minimun. Its a trade-off for not carving a top in the traditional way, but thats okay. I really want get on with completing this one and move on. -Vinny

[Acousticraft]

You need a thin clamping ring (caul) the outer shape of the guitar so it spreads the load evenly. I found thru trial and error to use a strip of flexible ply about 3" wide to cover the centre joint area where it sits on the centre block. It should be long enough to just fit inside your caul.

Do a dry run and clamp up with no glue first and clamp the centre block area to pull it down snug and then clamp the edges down evenly bit by bit. this will highlight any possible problems that may occur.

If you don't clamp the centre block area first, the pressure from clamping the edges will split the glued centre joint.

(I dont know whether your ply is one piece or not but it will take the strain off this area?) You need quite a number of clamps probably a dozen or more. Have these all ready to go when you do glue it will minimise the time it takes to clamp everything snug. My centre blocks were 3/8" thicker front and back in the middle than at the edges of my 335.

I was just thinking 3/16" is quite thick and you may need to steam the ply first so it will bend easily and clamp it down dry and leave it clamped for 24hrs then release the clamps and glue it.

Edited July 8, 2007 by Acousticraft

[axemannate]

I just got Jim English's book "Making a laminated hollow body guitar" and he starts by making a plaster mold of the back of an old hollow body. He then pours epoxy resin into it to make a male part of the mold, and pours epoxy resin on the male part to make the female part. Then he justs puts the veneneers in the mold and clamps away.

I highly recommend the book as it has revealed a lot of the mystery in building a hollow body type guitar for me. Hopefully i get started soon

you can find the book here: http://www.lmii.com/CartTwo/thirdproducts....Electric+Guitar